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Using air-gaps to replace conventional silicon dioxide as the insulators of through-silicon-vias (TSVs) has the possibility to improve the electrical performance and some thermal reliability issues of TSVs. This paper reports the implementation of TSVs with air-gap insulators by developing a polymer sacrificial technology. The sacrificial technology and the key fabrication processes are investigated in detail, including spin-coating of poly propylene carbonate (PPC) on the sidewalls of blind vias, copper chemical-mechanical polishing, PPC grinding, and PPC pyrolysis to form air-gaps. To address the technical challenge in coating thin and conformal PPC sacrificial claddings in blind vias, a vacuum-assisted solvent refilling technique is developed. Air-gap TSVs are successfully fabricated and the electrical performances are characterized. The accumulation capacitance of the air-gap TSVs is 48 fF, and the leakage current is as low as 1.22 pA at bias voltage of 20 V. Finite element simulation shows that air-gaps are able to reduce thermal stresses. The preliminary results demonstrate the feasibility of the sacrificial technology and the good electrical performance of air-gap TSVs. [ABSTRACT FROM AUTHOR]

Replacing silicon dioxide with polymers that have low dielectric constants as the insulation (liner) materials is of great help in reducing the capacitive coupling of through-silicon-vias and improving the reliability. This paper presents the fabrication of uniform poly propylene carbonate (PPC) polymer liners in high aspect ratio trenches by addressing the difficulty in coating PPC layers on via inner walls. A unique spin-coating method is developed by using vacuum treatment and solvent refill techniques for PPC liner formation for circular and annular trenches. Vacuum treatment and solvent refill facilitate PPC filling in high aspect ratio vias by preventing formation of air bubbles in the vias. By investigating the flow behaviors of PPC precursors and optimizing the spin-coating parameters, an optimal fabrication process is achieved. Using this newly developed technique as well as the optimized processing parameters, uniform PPC liners are successfully fabricated on the inner walls of circular vias with coating aspect ratio greater than 9:1 and the annular vias with filling aspect ratio of 24:1. [ABSTRACT FROM AUTHOR]

Low capacitance is critical to the electric performance of through-silicon-vias (TSVs). This paper reports the development of a low capacitance TSVs by replacing silicon dioxide insulation layers (liners) with benzocyclobutene (BCB) polymer. The BCB liner TSVs are fabricated by etching deep annular trenches on substrates, void-free filling the trenches with BCB polymer, selective etching the silicon post in the annular trenches, and filling the via with copper. Key fabrication processes including void-free BCB polymer filling in deep trenches, BCB chemical mechanical planarization, and selective etching of silicon post to BCB are developed. TSVs with BCB liners are successfully fabricated and the electrical performance is measured. The measurement results show that the capacitance of the BCB liner TSVs is around 42 fF, and the leakage currents to substrates and to neighboring TSVs are 2.2 pA and 1.1 pA at 10 V voltage, respectively. These preliminary results demonstrate the feasibility of the proposed fabrication technology and the efficacy of BCB liners in reducing TSV capacitance. [ABSTRACT FROM PUBLISHER]

Low capacitance is critical to the electric performance of through-silicon vias (TSVs). This paper reports the development and electrical characterization of ultralow-capacitance TSVs which use air gaps to replace the conventional silicon dioxide as the insulation layers. The air-gap TSVs are successfully fabricated by developing a sacrificial technology which uses void-free filling and selective etching of an annular benzocyclobutene polymer cladding that surrounds copper plugs. The capacitance and the leakage current are tested to characterize the electrical performance. The lowest effective dielectric constant of the air enables the capacitance of the air-gap TSVs to be as low as 24 fF, and the capacitance density is more than one order of magnitude lower than that of conventional \Si\O2 liner TSVs. The leakage current to the substrate is \3 \times \10^-13\ \A at 40 V, and no leakage current degradation occurs after a 40-cycle thermal shock test. The preliminary results demonstrate the new air-gap structure and the efficacy of air gaps in reducing TSV capacitance. [ABSTRACT FROM PUBLISHER]

Etching of thick nonphotosensitive benzocyclobutene (BCB) was investigated using a high density SF6/O2 plasma with an inductively coupled plasma (ICP) etcher. The effects of SF6 concentration on etching characteristics, including etching rate, anisotropy, and residue, are fully discussed in this article. Moreover, experiments were designed and carried out to study the causes of BCB etching residue. A grasslike etching residue was observed for low SF6 concentration at the bottom of BCB patterns with a SiO2/SixN layer and the BCB patterns cured on a N2-purged hotplate, while residue-free etching is obtained for the BCB patterns cured in a N2-purged vacuum chamber. A high SF6 concentration and exclusion of O2 during hard curing are important to prevent the grasslike etching residue. A highly anisotropic and residue-free etching of thick (∼13 μm) BCB is achieved for BCB cured in a N2-purged vacuum chamber at 250 °C for 1 h and with a pure SF6 plasma under etching conditions of 700 W ICP power, 100 W reactive ion etching power, 15 mTorr chamber pressure, and 50 SCCM (SCCM denotes cubic centimeter per minute at STP) gas flow. Mechanisms for the dependence of the etching characteristics on SF6 concentration are discussed. [ABSTRACT FROM AUTHOR]

This letter reports for the first time the fabrication and characterization of through-silicon vias (TSVs) using air-gap insulators to enable high-performance 3-D integration. To address the challenge in fabricating extremely high-aspect-ratio air gaps, a CMOS-compatible sacrificial technology based on pyrolysis of poly (propylene carbonate) has been developed, upon which air-gap TSVs have been successfully achieved. The measured capacitance density and leakage current density of air-gap TSVs are 1.22 \nF/cm^2 and 10 \nA/cm^2, respectively, about one order and two orders lower in magnitude than TSVs using \SiO2 insulators. [ABSTRACT FROM PUBLISHER]